FIG. 1 schematically illustrates an example of structure of array antenna device in a conventional communication system.
Referring to FIG. 1, it will be assumed that the communication system is a frequency division duplexing (FDD) communication system which uses a code division multiple access (CDMA) scheme.
Referring to FIG. 1, the array antenna device includes N+1 antennas, i.e., an additional antenna 110 and N array antennas, i.e., an array antenna #1 120-1, an array antenna #2 120-2, . . . , an array antenna # n 120-n , . . . , an array antenna # N 120-N, N+1 circulators, i.e., a circulator #0 130-0, a circulator #1 130-1, . . . , a circulator # n 130-n, . . . , a circulator # N 130-N, N+1 radio frequency (RF) chains, i.e., N+1 RF transmit chains, i.e., a RF transmit chain #0 140-0, a RF transmit chain #1 140-1, . . . , a RF transmit chain #n 140-n, . . . , a RF transmit chain #N 140-N, N+1 RF receive chains, i.e., a RF receive chain #0 150-0, a RF receive chain #1 150-1, . . . , a RF receive chain #n, a RF receive chain #N 150-N, and a calibration processor 160.
The additional antenna 110 is an antenna which is used for performing a calibration operation on the array antenna device in a an FDD scheme based communication system which uses the CDMA scheme, and the array antenna device performs the calibration operation using a phenomenon in which signals transmitted from antennas are coupled among the antennas if a calibration signal is transmitted in the array antenna device.
As illustrated in FIG. 1, a RF chain, i.e., a RF transmit chain and a RF receive chain are connected to each of antennas included in the array antenna device, so the array antenna device becomes a fully digital system. Here, it will be assumed that a transmit frequency which the array antenna device uses is “ftx”, and a receive frequency which the array antenna device uses is “frx”.
It will be assumed that a phase difference which occurs when a calibration signal is transmitted/received between the additional antenna 110 and each of the array antenna #1 120-1, the array antenna #2 120-2, . . . , the array antenna # n 120-n , . . . , the array antenna # N 120-N has been previously measured. Here, a undesired complex gain is not almost changed since locations of the additional antenna 110, the array antenna #1 120-1, the array antenna #2 120-2, . . . , the array antenna # n 120-n, . . . , the array antenna # N 120-N are fixed, the additional antenna 110, the array antenna #1 120-1, the array antenna #2 120-2, . . . , the array antenna # n 120-n, . . . , the array antenna # N 120-N are passive, or a wired environment neighboring the array antenna # n 120-n, . . . , the array antenna # N 120-N are fixed, the additional antenna 110, the array antenna #1 120-1, the array antenna #2 120-2, . . . , the array antenna # n 120-n, . . . , the array antenna # N 120-N are passive, so the phase difference may be previously measured.
A transmit path calibration operation of the array antenna device in FIG. 1 is performed through processes (a1) to (c1), and a detailed description will be followed.
(a1) The calibration processor 160 generates a calibration signal, and outputs the generated calibration signal to the RF transmit chain #1 140-1, . . . , the RF transmit chain #n 140-n, . . . , the RF transmit chain #N 140-N. Each of the RF transmit chain #1 140-1, . . . , the RF transmit chain #n 140-n, . . . , the RF transmit chain #N 140-N modulates the calibration signal output from the calibration processor 160 corresponding to the transmit frequency ftx to transmit the modulated signal.
(b1) The RF receive chain #0 150-0 receives a signal in which signals transmitted from the RF transmit chain #1 140-1, . . . , the RF transmit chain #n 140-n, . . . , the RF transmit chain #N 140-N are coupled, and the calibration processor 160 separates a data signal which is linearly combined with a calibration signal transmitted from each of the array antenna #1 120-1, the array antenna #2 120-2, . . . , the array antenna # n 120-n, . . . , the array antenna # N 120-N as well as a data signal into a signal per antenna path.
(c1) The calibration processor 160 calculates a calibration factor for each transmit path from the separated calibration signal per antenna path, and a detailed description will be followed.
A signal received in the RF receive chain #0 150-0 in the (b1) process may be expressed as Equation (1).y(t)=ΣnMcn(t)ej(ϕcrx+ϕcn+ϕntx)+Σn=1MΣm=1Msn,m(t)ej(ϕcrx+ϕcn+ϕntx)zc(t)  Equation (1)
In Equation (1), cn(t) denotes a calibration signal transmitted from the nth array antenna, zc(t) denotes an additive white Gaussian noise (AWGN) in a calibration antenna path, ϕcrx denotes a receive phase characteristic of the additional array antenna, ϕntx denotes a transmit phase characteristic of the nth array antenna, ϕcn denotes phase delay between the additional array antenna and the nth array antenna, and sn,m(t) denotes the mth data signal from the nth array antenna.
A phase difference between the jth array antenna and the kth array antenna in the (b1) process may be expressed as Equation (2).
                              ρ          kj          tx                =                                            ρ              k              tx                        /                          ρ              j              tx                                =                                                    1                T                            ⁢                                                ∫                  T                                ⁢                                                      y                    ⁡                                          (                      t                      )                                                        ⁢                                                            c                      k                      *                                        ⁡                                          (                      t                      )                                                        ⁢                                      dt                    /                                          1                      T                                                        ⁢                                                            ∫                      T                                        ⁢                                                                  y                        ⁡                                                  (                          t                          )                                                                    ⁢                                                                        c                          j                          *                                                ⁡                                                  (                          t                          )                                                                    ⁢                      dt                                                                                            =                                                            e                                      j                    ⁡                                          (                                                                        ϕ                          c                          rx                                                +                                                  ϕ                          ck                                                +                                                  ϕ                          k                          tx                                                                    )                                                                                        e                                      j                    ⁡                                          (                                                                        ϕ                          c                          rx                                                +                                                  ϕ                          cj                                                +                                                  ϕ                          j                          tx                                                                    )                                                                                  =                              e                                  j                  ⁡                                      (                                                                  ϕ                        k                        tx                                            -                                              ϕ                        j                        tx                                                              )                                                                                                          Equation        ⁢                                  ⁢                  (          2          )                    
In Equation (2), T denotes a period of a test signal, and this is why ej(ϕck−ϕcj) may be previously compensated.
So, a transmit calibration factor may be detected using the phase ρkjtx between the jth array antenna and the kth array antenna.
Further, a receive path calibration operation of an array antenna device in FIG. 1 is performed through processes (a2) to (c2), and a detailed description will be followed.
(a2) The RF transmit chain #0 140-0 modulates the calibration signal output from the calibration processor 160 corresponding to a receive frequency frx to transmit the modulated signal.
(b2) The RF receive chain #1 150-1 to the RF receive chain #N 150-N receive the calibration signal transmitted from the RF transmit chain #0 140-0 in the (a2) process in a coupling form, and the calibration processor 160 separates the calibration signal which is combined with digital signals received in the RF receive chain #1 150-1 to the RF receive chain #N 150-N.
(c2) The calibration processor 160 calculates a calibration factor for each receive path from the separated calibration signal, and a detailed description will be followed.
A signal which is received through the nth array antenna in the (b2) process may be expressed as Equation (3).rn(t)=c(t)ej(ϕctx+ϕcn+ϕnrx)+Σm=1Msn,m(t)ejϕnrx+zn(t)  Equation (3)
In Equation (3), cn(t) denotes a test signal of a RF transmit chain which is connected to the nth array antenna, ϕctx denotes a transmit phase characteristic of the RF transmit chain which is connected to the nth array antenna, ϕcrx denotes a receive phase characteristic of the nth array antenna, ϕcn denotes phase delay between the additional array antenna and the nth array antenna, sn,m(t) denotes the mth data signal from the nth array antenna, and zn(t) denotes an AWGN from the nth array antenna path.
A phase difference between the jth array antenna and the kth array antenna in the (b2) process may be expressed as Equation (4).
                              ρ          kj          rx                =                                            ρ              k              rx                        /                          ρ              j              rx                                =                                                    1                T                            ⁢                                                ∫                  T                                ⁢                                                                            r                      j                                        ⁡                                          (                      t                      )                                                        ⁢                                                            c                      *                                        ⁡                                          (                      t                      )                                                        ⁢                                      dt                    /                                          1                      T                                                        ⁢                                                            ∫                      T                                        ⁢                                                                                            r                          k                                                ⁡                                                  (                          t                          )                                                                    ⁢                                                                        c                          *                                                ⁡                                                  (                          t                          )                                                                    ⁢                      dt                                                                                            =                                                            e                                      j                    ⁡                                          (                                                                        ϕ                          c                          tx                                                +                                                  ϕ                          ck                                                +                                                  ϕ                          k                          rx                                                                    )                                                                                        e                                      j                    ⁡                                          (                                                                        ϕ                          c                          tx                                                +                                                  ϕ                          cj                                                +                                                  ϕ                          j                          rx                                                                    )                                                                                  =                              e                                  j                  ⁡                                      (                                                                  ϕ                        k                        rx                                            -                                              ϕ                        j                        rx                                                              )                                                                                                          Equation        ⁢                                  ⁢                  (          4          )                    
In Equation (4), T denotes a period of a test signal, and this is why e j(ϕck−ϕcj) may be previously compensated.
An example of structure of array antenna device in a conventional communication system has been described with reference to FIG. 1, and another example of structure of array antenna device in a conventional communication system will be described with reference to FIG. 2.
FIG. 2 schematically illustrates another example of structure of array antenna device in a conventional communication system.
Referring to FIG. 2, the array antenna device performs a calibration operation using a signal which is acquired by internally circulating a calibration signal using a coupler. So, the array antenna device in FIG. 2 uses a relatively complex RF network.
The array antenna device includes N array antennas, i.e., an array antenna #1 210-1, an array antenna #2 210-2, . . . , an array antenna # N 210-N, . . . , an array antenna # N 120-N, N circulators, i.e., a circulator #1 220-1, . . . , a circulator #2 220-2, . . . , a circulator # N 220-N, N directional couplers (DCs), i.e., a DC #1 230-1, a DC #2 230-2, . . . , a DC #N 230-N, a frequency converter (FC) 240, a plurality of switches, i.e., a SW#1 250-1, a SW#2 250-2, a SW#3 250-3, . . . , N RF transmit chains, i.e., a RF transmit chain #1 260-1, a RF transmit chain #2 260-2, . . . , a RF transmit chain #N 260-N, N RF receive chains, i.e., a RF receive chain #1 270-1, a RF receive chain #2 270-2, . . . , a RF receive chain #N 270-N, and an adaptive & calibration processor 280.
Further, f1 denotes a transmitting operation frequency, f2 denotes a receiving operation frequency, Q denotes a undesired complex gain which occurs by the FC 240, Riexp(jθi) denotes a undesired complex gain which occurs in the ith receiver, i.e., the ith RF receive chain, and Tiexp(jΔi) denotes a undesired complex gain which occurs in the ith transmitter, i.e., the ith RF transmit chain.
A transmit path calibration operation of the array antenna device in FIG. 2 is performed through processes (a1) to (c1), and a detailed description will be followed.
(a1) A signal which is transmitted through each of the RF transmit chain #1 260-1, the RF transmit chain #2 260-2, . . . , the RF transmit chain #N 260-N is coupled to each of the DC #1 230-1, the DC #2 230-2, . . . , the DC #N 230-N, and the coupled signal is transferred to the SW1 250-1.
(b1) The SW1 250-1 transfers the signal which is transferred from each of the DC #1 230-1, the DC #2 230-2, . . . , the DC #N 230-N to the FC 240. The FC 240 converts a transmit operating frequency of the signal which is transferred from each of the DC #1 230-1, the DC #2 230-2, . . . , the DC #N 230-N to a receive operating frequency, and transfers the converted signal to the RF receive chain #1 270-1.
(c1) The array antenna device may acquire a gain as Equation (5) through the operations.R1 exp(jθ1)QTi exp(jΔi) for i=1, . . . , N  Equation (5)
(d1) A transmit calibration factor may be acquired as Equation (6) using the gain which is acquired in the (c1) process.
                                          H            i                    =                                                                      R                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              θ                        1                                                              )                                                  ⁢                                  QT                  i                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              Δ                        i                                                              )                                                                                                R                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              θ                        1                                                              )                                                  ⁢                                  QT                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              Δ                        1                                                              )                                                                        =                                                            T                  i                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              Δ                        i                                                              )                                                                                                T                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              Δ                        1                                                              )                                                                                      ⁢                                  ⁢                                            for              ⁢                                                          ⁢              i                        =            1                    ,          …          ⁢                                          ,          N                                    Equation        ⁢                                  ⁢                  (          6          )                    
Further, a receive path calibration operation of an array antenna device in FIG. 2 is performed through processes (a2) to (c2), and a detailed description will be followed.
(a2) The signal transmitted from the RF transmit chain #1 260-1 is coupled by the DC#1 230-1, and the coupled signal is transferred to the SW 1 250-1. The SW 1 250-1 transfers the signal which is transferred from the DC#1 230-1 to the FC 240. The FC 240 frequency converts the signal output from the SW1 250-1.
(b2) The signal which is frequency converted in the FC 240 is transferred to the SW2 250-2, and the SW2 250-2 transfers the frequency converted signal to the RF receive chain #1 270-1, the RF receive chain #2 270-2, . . . , the RF receive chain #N 270-N.
(c2) The array antenna device may acquire a gain as Equation (7) through the operations.Ri exp(jθi)QT1 exp(jΔ1) for i=1, . . . , N  Equation (7)
(d2) A receive calibration factor may be acquired as Equation (8) using the gain which is acquired in the (c2) process.
                                          P            i                    =                                                                      R                  i                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              θ                        i                                                              )                                                  ⁢                                  QT                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              Δ                        1                                                              )                                                                                                R                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              θ                        1                                                              )                                                  ⁢                                  QT                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              Δ                        1                                                              )                                                                        =                                                            R                  i                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              θ                        i                                                              )                                                                                                R                  1                                ⁢                                  exp                  ⁡                                      (                                          j                      ⁢                                                                                          ⁢                                              θ                        1                                                              )                                                                                      ⁢                                  ⁢                                            for              ⁢                                                          ⁢              i                        =            1                    ,          …          ⁢                                          ,          N                                    Equation        ⁢                                  ⁢                  (          8          )                    
In the array antenna device in FIG. 1, since an antenna which is additionally equipped for a calibration operation of the array antenna device, i.e., an additional antenna, may be for only the calibration operation, the additional antenna does not help to enhance a direct communication performance such as data rate, and the like, so the additional antenna is a redundancy in view of communication performance enhancement. The array antenna device in FIG. 1 considers a fully digital system in which a transmitting/receiving (TR) module equips with a RF chain, so it may be difficult that the calibration operation in FIG. 1 is applied to a sub-array based array antenna device.
Further, the array antenna device in FIG. 2 uses a RF network with relatively complex structure for calibration.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.